Global navigation satellite systems (GNSS) are broadly defined to include GPS (U.S.), Galileo (proposed), GLONASS (Russia), Beidou (China), IRNSS (India, proposed), QZSS (Japan, proposed) and other current and future positioning technologies using signals from satellites, with or without augmentation from terrestrial sources. Information from GNSS is being increasingly used for computing a user's positional information (e.g., a location, a speed, a direction of travel, etc.).
In GNSS, multiple satellites may be present, with each transmitting a GNSS signal. A received signal at a GNSS receiver contains one or more of the transmitted GNSS signals. To obtain the information from the respective transmitted signals, the GNSS receiver performs a signal acquisition/tracking procedure. More specifically, the GNSS receiver searches for the corresponding transmitted signals in the received signal and then locks onto them for subsequent tracking of the corresponding satellites to receive the satellite information.
However, GNSS receivers are affected by interference in the form of spurious signals. These signals are caused by other wireless transmitters and receivers co-existing in the cell-phone platform or other noise sources including the digital processors of the GNSS receiver. Spurious signals or Spurs considered in this description are narrow-band interferers in the GNSS signal frequency band. The term spur and spurious signal has been used interchangeably in this disclosure.
Spurs degrade the overall sensitivity of the GNSS receiver. More importantly, the presence of spurs in the received spectrum also results in erroneous determination of position and velocity of a user by the GNSS receiver. Modern multi-constellation GNSS receivers are highly susceptible to this problem due to their wide RF frequency spectrum and presence of other radios on a shared chip or circuit board. Thus, there is a requirement for a GNSS receiver that mitigates the effect of spurious signals.